U.S. patent application number 13/777909 was filed with the patent office on 2013-09-19 for tennis racket and method for manufacturing the same.
This patent application is currently assigned to YONEX KABUSHIKI KAISHA. The applicant listed for this patent is YONEX KABUSHIKI KAISHA. Invention is credited to Tomoya Iwasawa, Shinji Saito, Junya Suetake.
Application Number | 20130244817 13/777909 |
Document ID | / |
Family ID | 47754338 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130244817 |
Kind Code |
A1 |
Saito; Shinji ; et
al. |
September 19, 2013 |
TENNIS RACKET AND METHOD FOR MANUFACTURING THE SAME
Abstract
A tennis racket includes a frame that surrounds a hitting face
for hitting a ball, wherein a foam material is provided inside two
side portions of the frame on opposite sides of a predetermined
area of the hitting face, and the two side portions of the frame
have a strength that is higher than a strength of another portion
of the frame.
Inventors: |
Saito; Shinji; (Niigata,
JP) ; Suetake; Junya; (Niigata, JP) ; Iwasawa;
Tomoya; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
YONEX KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Assignee: |
YONEX KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
47754338 |
Appl. No.: |
13/777909 |
Filed: |
February 26, 2013 |
Current U.S.
Class: |
473/521 ;
156/217 |
Current CPC
Class: |
A63B 2209/02 20130101;
B29C 44/146 20130101; A63B 49/03 20151001; B29C 70/865 20130101;
A63B 49/02 20130101; A63B 49/11 20151001; A63B 49/10 20130101; A63B
60/54 20151001; B29C 70/446 20130101; B29L 2031/5245 20130101; Y10T
156/1036 20150115 |
Class at
Publication: |
473/521 ;
156/217 |
International
Class: |
A63B 49/02 20060101
A63B049/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2012 |
JP |
2012-40538 |
Claims
1. A tennis racket comprising: a frame that surrounds a hitting
face for hitting a ball; wherein a foam material is provided inside
two side portions of the frame on opposite sides of a predetermined
area of the hitting face, and the two side portions of the frame
have a strength that is higher than a strength of another portion
of the frame.
2. A tennis racket according to claim 1, wherein a foam material
for filling that is different from the foam material is provided
inside the another portion of the frame.
3. A tennis racket according to claim 1, wherein the foam material
is provided inside the another portion of the frame, and an amount
of the foam material in the two side portions is different from an
amount of the foam material in the another portion.
4. A tennis racket according to claim 1, wherein the frame has a
frame portion that surrounds the hitting face on one end side, and
has a grip portion on another end side, and the predetermined area
is an area on the one end side than substantially a middle of the
hitting face.
5. A tennis racket according to claim 4, wherein when a position of
the one end of the frame portion is set at 0 degrees relative to a
center of the hitting face, the foam material is provided in a
range of 20 degrees to 60 degrees of the frame portion.
6. A method for manufacturing a tennis racket including a frame
having a first strength and a second strength that is higher than
the first strength, comprising the steps of: arranging a foam
material on a resin sheet in an area that corresponds to the second
strength; forming a sheet tube by wrapping the resin sheet, on
which the foam material is arranged, into a cylindrical shape; and
forming a frame in which the resin sheet and the foam material are
integrally molded, by bending the sheet cylinder to be set in a
die, and then causing the foam material to undergo foaming.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority upon Japanese Patent
Application No. 2012-40538 filed on Feb. 27, 2012, which is herein
incorporated by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to a tennis racket and a
method for manufacturing a tennis racket.
[0004] 2. Related Art
[0005] A tennis racket includes a frame that surrounds a hitting
face for hitting a ball. There has also been proposed a tennis
racket in which the frame is formed hollow with the entire hollow
portion is uniformly filled with foam material (e.g., see Japanese
Patent Application Laid-Open Publication No. 6-105923).
[0006] The area of the hitting face that is frequently used differs
from player to player in some cases. For example, top players
(advanced players) tend to frequently use the area of the hitting
face at the tip side (side opposite to the grip portion) than the
substantially central portion (sweet spot). For this reason, there
is demand for an increase in particularly rigidity (strength) and
vibration absorption in the portions of the frame that correspond
to the area that is frequently used.
[0007] Incidentally, since a foam material is formed uniformly
inside the frame of tennis rackets such as those described above,
it has been difficult to increase rigidity and vibration absorption
at specific positions in the frame. Increasing rigidity by
providing foam material to the entire frame leads to a problem of
an increase in repulsive force (due to a decrease in frame flexure)
and a decline in control when hitting the ball (ball control), and
also leads to a problem of difficulty in weight reduction.
SUMMARY OF THE INVENTION
[0008] The present invention has been made in view of these
circumstances, and an object thereof is to provide a tennis racket
that allows improvement in rigidity and vibration absorption at a
desired position and allows improvement in ball control and
reduction in weight, as well as a method for manufacturing the
same.
[0009] A tennis racket according to a main invention for achieving
the aforementioned object is a tennis racket including a frame that
surrounds a hitting face for hitting a ball, wherein a foam
material is provided inside two side portions of the frame on
opposite sides of a predetermined area of the hitting face, and the
two side portions of the frame have a strength that is higher than
a strength of another portion of the frame.
[0010] According to the tennis racket of the present invention,
rigidity and vibration absorption at a desired position in the
frame can be improved, and ball control can be improved and the
weight thereof can be reduced as well.
[0011] Other features of the present invention will become clear
from the explanation in the present specification and the
description of the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a front view of a tennis racket 1 according to an
embodiment of the present invention;
[0013] FIG. 2 is a side view of the tennis racket 1 according to
the embodiment of the present invention;
[0014] FIG. 3A is a schematic diagram showing a method for
manufacturing the tennis racket 1;
[0015] FIG. 3B is another schematic diagram showing the method for
manufacturing the tennis racket 1;
[0016] FIG. 3C is another schematic diagram showing the method for
manufacturing the tennis racket 1;
[0017] FIG. 3D is another schematic diagram showing the method for
manufacturing the tennis racket 1;
[0018] FIG. 4A is a cross-sectional view taken along A-A in FIG.
3B;
[0019] FIG. 4B is a cross-sectional view taken along B-B in FIG.
3B;
[0020] FIG. 5 is a schematic diagram showing an aspect of a
hardness test performed with the foam material alone;
[0021] FIG. 6 is a schematic diagram showing an aspect of a test
regarding the amount of cross-section deformation of the
racket;
[0022] FIG. 7 is a schematic diagram showing an aspect of a racket
bending test; and
[0023] FIG. 8 is an illustrative diagram of a modified example.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
Summary of Disclosure
[0024] At least the following matters will be made clear by the
explanation in the present specification and the description of the
accompanying drawings.
[0025] Specifically, the tennis racket that will be made clear is a
tennis racket including a frame that surrounds a hitting face for
hitting a ball, wherein a foam material is provided inside two side
portions of the frame on opposite sides of a predetermined area of
the hitting face, and the two side portions of the frame have a
strength that is higher than a strength of another portion of the
frame.
[0026] According to such tennis racket, rigidity and vibration
absorption at a desired position in the frame can be improved, and
ball control can be improved and the weight thereof can be reduced
as well.
[0027] In the above tennis racket, a foam material for filling that
is different from the foam material is provided inside the another
portion of the frame. Also, the foam material is provided inside
the another portion of the frame, and an amount of the foam
material in the two side portions is different from an amount of
the foam material in the another portion.
[0028] According to such tennis racket, a hollow portion can be
prevented from being made to the frame, and foreign particles can
be prevented from entering into the frame.
[0029] In the above tennis racket, it is desirable that the frame
has a frame portion that surrounds the hitting face on one end
side, and has a grip portion on another end side, and the
predetermined area is an area on the one end side than
substantially a middle of the hitting face.
[0030] According to such tennis racket, optimum hitting
characteristics (e.g., control) can be obtained when used by a
player who often uses one end side of the hitting face (e.g., a top
player).
[0031] In the above tennis racket, it is desirable that when a
position of the one end of the frame portion is set at 0 degrees
relative to a center of the hitting face, the foam material is
provided in a range of 20 degrees to 60 degrees of the frame
portion.
[0032] According to such tennis racket, it is possible to increase
rigidity and vibration absorption when hitting the ball with one
end side of the hitting face.
[0033] Also, a method for manufacturing a tennis racket including a
frame having a first strength and a second strength that is higher
than the first strength, including the steps of arranging a foam
material on a resin sheet in an area that corresponds to the second
strength, forming a sheet tube by wrapping the resin sheet, on
which the foam material is arranged, into a cylindrical shape, and
forming a frame in which the resin sheet and the foam material are
integrally molded, by bending the sheet cylinder to be set in a
die, and then causing the foam material to undergo foaming.
Embodiments
Example of Racket Configuration
[0034] A configuration example of a tennis racket 1 according to
the present invention will be described below with reference to
FIGS. 1 and 2. FIG. 1 is a front view of the tennis racket 1
according to the present embodiment. FIG. 2 is a side view of the
tennis racket 1 according to the present embodiment. Note that the
upper side (with respect to the figure) of the tennis racket 1
shown in FIGS. 1 and 2 is called the tip side, and the lower side
is called the base side.
[0035] As shown in FIG. 1, the tennis racket 1 of the present
embodiment includes a frame 10 that is configured by a face portion
12 (corresponding to the frame portion), a shaft portion 13, and a
grip portion 14.
[0036] The face portion 12 is provided in the top portion of the
tennis racket 1 and is formed in a substantially elliptical shape.
Insertion holes (not shown) for inserting a string are provided, in
an inner circumferential portion and an outer circumferential
portion of the face portion 12 (and a later-described yoke portion
16), so as to communicate the inner and outer portions, and
therefore a string that is inserted into the insertion hole at the
outer circumferential portion can be taken out from the insertion
hole at the inner circumferential portion. A plurality of these
insertion holes (not shown) are provided in a line along the
circumferential direction of the face portion 12. When a string is
strung between the insertion holes, the string segments cross each
other in a grid form within the face portion 12. A substantially
elliptical hitting face (face for hitting a ball) is thus formed
within the face portion 12. Also, a sweet spot S shown in FIG. 1 is
a substantially middle area of the hitting face that includes the
center C of the hitting face, and the size of this area is
dependent on the shape of the hitting face (in other words, the
shape of the face portion 12 seen from the front).
[0037] The shaft portion 13 is a portion that connects the face
portion 12 and the grip portion 14, and is formed so as to branch
out into two from the grip portion 14 toward the face portion 12.
Also, the yoke portion 16 that configures a portion of the hitting
face is provided at the boundary between the face portion 12 and
the shaft portion 13.
[0038] The grip portion 14 is the portion that is gripped by the
player, and is positioned in the base end portion of the tennis
racket 1. Normally, grip tape 20 is wound around the grip portion
14 of the tennis racket 1. The grip tape 20 absorbs the shock
generated when hitting a ball, and also improves the grip.
[0039] Note that a fiber-reinforced resin, which is obtained by
impregnating fiber with resin such as mainly carbon fiber, glass
fiber, organic fiber, ceramic fiber, or the like, is used to form
the frame 10 (the face portion 12, the shaft portion 13, and the
grip portion 14) of the tennis racket 1. In the present embodiment,
the frame 10 uses a thermosetting fiber-reinforced resin whose
reinforcing fiber is carbon fiber, and as will be described later,
the frame 10 is formed by rolling up the fiber-reinforced resin in
a sheet form (a carbon sheet) so as to form a hollow bar body,
bending the bar body into the shape of the tennis racket 1, and
then fitting the bar body into a predetermined die and performing
heat and pressure molding.
[0040] The frame 10 of the present embodiment is also provided with
a foam material 30 in the areas indicated by hatching (referred to
hereinafter as hatched portions) in the face portion 12 that
surrounds the hitting face. As shown in FIG. 1, the portions where
the foam material 30 is provided are areas on respective sides (two
side portions) of the face portion 12 that are on opposite sides of
a predetermined area of the hitting face on the tip side than the
sweet spot S. More specifically, assuming that the tip (upper end)
position of the face portion 12 is 0 degrees relative to the center
C of the hitting face, the foam material 30 is provided inside the
area of the face portion 12 that corresponds to the range between
angle .theta..sub.1 (e.g., 20 degrees) and angle .theta..sub.2
(e.g., 60 degrees). Note that the foam material 30 is not provided
in portions other than the hatched portions of the frame 10
(referred to hereinafter as non-hatched portions)
[0041] Also, as shown in FIG. 2, the width (length in the normal
direction relative to the hitting face) W.sub.2 of the frame 10 in
the hatched portions is made greater than the width W.sub.1 of the
frame 10 in the non-hatched portions. Specifically, the width
W.sub.1 is 20 mm, and the width W.sub.2 is 22 mm. Since the width
of the frame 10 in the hatched portions is made greater than that
in the non-hatched portions in this way, more of the foam material
30 can be provided in the frame 10, and the strength can be
increased even more.
[0042] The following describes the reason why the foam material 30
is provided to the frame 10 (the face portion 12) only partially in
this way. As one example, top players (advanced players) tend to
frequently use the area on the tip side of the hitting face than
the sweet spot S. For this reason, there is a demand to increase
particularly rigidity (strength) and vibration absorption in the
areas of the frame 10 that correspond to this area. Since the foam
material 30 is provided in these areas in the present embodiment,
it is possible to improve rigidity and vibration absorption when
hitting a ball with the tip side of the hitting face.
[0043] Also, if the foam material 30 were uniformly provided in the
entire interior of the frame 10, the overall strength would
increase, thus leading to a risk of a decrease in flexure, an
increase in repulsive force, and a decline in ball control.
Furthermore, the overall weight of the frame 10 would increase,
thus making a reduction in weight difficult. In contrast to this,
with the present embodiment, the foam material 30 is provided on
the two sides (the hatched portions) of the frame 10 (the face
portion 12) that are on opposite sides of a predetermined area on
the tip side than the sweet spot S, and the foam material 30 is not
provided in the other areas (the non-hatched portions), thus
allowing the face portion 12 to flex to an appropriate amount when
hitting a ball. This enables to improve control when hitting a
ball. This also makes a reduction in weight possible.
Racket Manufacturing Method
Present Embodiment
[0044] A method for manufacturing the tennis racket 1 of the
present embodiment will be described below with reference to FIGS.
3A to 3D. FIGS. 3A to 3D are schematic diagrams showing the method
for manufacturing the tennis racket 1.
[0045] The method for manufacturing the tennis racket 1 of the
present embodiment has a foam material arranging step, a sheet tube
forming step, a bending step, and a die molding step.
<Foam Material Arranging Step>
[0046] First, as shown in FIG. 3A, a carbon sheet 44 (which
corresponds to a resin sheet) of prepreg fiber-reinforced resin
(FRP) mainly made of carbon fiber is prepared, and the foam
material 30 is arranged in areas that correspond to the hatched
portions in FIG. 1. The foam material 30 is obtained by mixing a
resin-based adhesive and a thermally expandable foam material, and
forming the mixture into a sheet shape.
[0047] Note that in FIG. 3A, the midpoint of the carbon sheet 44 in
the lengthwise direction (left-right direction in the figure) will
become the tip of the frame 10 (the face portion 12) of the tennis
racket 1, and therefore positions on the frame 10 of the tennis
racket 1 can be specified in advance based on the distance from the
midpoint. In the present embodiment, the size of the sheets of the
foam material 30 and the positions where they are arranged on the
carbon sheet 44 are set such that the foam material 30 is provided
to the hatched portions of the frame 10 in FIG. 1.
<Sheet Tube Forming Step>
[0048] Next, as shown in FIG. 3A, a tube 42 is fitted around a
mandrel 40, and the carbon sheet 44 having the foam material 30
arranged thereon is wound around the tube 42. Note that the mandrel
40 is a round bar-shaped member (cored bar) whose length
corresponds to the entire length of the frame 10 (the face portion
12, the shaft portion 13, and the grip portion 14) of the tennis
racket 1. Also, the tube 42 is a flexible resin tube (e.g., a nylon
tube).
[0049] The mandrel 40 is then removed, and thus a cylindrical tube
body (referred to hereinafter as a sheet tube 100) is formed as
shown in FIG. 3B.
[0050] FIG. 4A is a cross-sectional view taken along A-A in FIG.
3B, and FIG. 4B is a cross-sectional view taken along B-B in FIG.
3B. As shown in FIG. 4A, in the A-A cross-section of the sheet tube
100, the foam material 30 is arranged on the outside of the tube
42. The carbon sheet 44 is then wound on the outside of the foam
material 30. In contrast, as shown in FIG. 4B, in the B-B
cross-section of the sheet tube 100, the carbon sheet 44 is wound
on the outside of the tube 42, and the foam material 30 is not
provided.
<Bending Step>
[0051] As shown in FIG. 3C, the sheet tube 100 is bent so as to
conform to the shape of the frame 10 (the face portion 12, the
shaft portion 13, and the grip portion 14) of the tennis racket 1.
Also, the yoke portion 16, which is formed using a configuration
similar to that of the sheet tube 100, is attached in the border
portions between the face portion 12 and the shaft portion 13, and
a carbon sheet 18 is wound around the border portions. Note that
the foam material 30 maybe provided inside the yoke portion 16.
<Die Molding Step>
[0052] The sheet tube 100 bent in the shape of the frame 10 and the
yoke portion 16 attached to the sheet tube 100 are set in a die 50
as shown in FIG. 3D. Heating is then performed, and air is
introduced into the tube 42 through the opening at the end (base)
of the grip portion 14 portion of the sheet tube 100. The sheet
tube 100 undergoes plastic deformation due to being heated, and at
this time, the carbon sheet 44 is pushed and spread outward due to
expansion of the tube 42, and the carbon sheet 44 is pressed
against the die 50. The plastically deformed sheet tube 100 is thus
molded into a shape that conforms to the die 50. Note that although
the foam material 30 expands (foams) at this time due to being
heated, this expansion is suppressed due to being subjected to air
pressure from the tube 42. The foam material 30 then expands when
the air pressure inside the tube 42 is released. Accordingly, in
the areas (hatched portions) where the foam materials 30 are
formed, the tube 42 is pressed into the surrounding foam material
30, and the interior of the frame 10 is filled with the foam
material 30. This results in the molding of the frame 10 in which
the carbon sheet 44 and the foam material 30 are integrated.
Comparative Example
[0053] The following describes a method for manufacturing a tennis
racket according to a comparative example. In this comparative
example, a liquid-form foam material that has a high expansion
ratio (e.g., urethane) is injected into a heat-molded hollow frame
through an opening at the base of the grip portion (end portion of
the hollow portion), and then is caused to undergo foaming. Due to
such foam material (the foam material used in this comparative
example being referred to hereinafter as the foam material 30')
undergoing foaming, the foam material 30' is uniformly provided
inside the entire the frame 10.
[0054] In contrast, with the present embodiment, the sheets of the
foam material 30 are arranged on the carbon sheet 44 before the
sheet tube 100 is formed, thus enabling to provide the foam
material 30 easily in arbitrary areas of the frame 10 by changing
the size and arrangement position of the foam material 30.
Foam Material Characteristics
[0055] The following describes a comparison of characteristics
(e.g., hardness) of the foam material 30 according to the present
embodiment and the foam material 30' according to the comparative
example. Note that as described above, the foam material 30 is
formed by mixing a resin-based adhesive and a thermally expandable
foam material, and the foam material 30' is a highly expandable
urethane foam material.
[0056] The following experiments were performed on cases with the
foam materials alone and with them formed inside the frame 10. The
results of these experiments are described below.
<Foam Material Hardness Test>
Test Method
[0057] FIG. 5 is a schematic diagram showing aspects of a hardness
test performed on the foam material alone. Test pieces (samples)
having vertical and horizontal lengths of 20 mm and a height of 5
mm were created using the respective foam materials (alone) in the
foamed state, and the amount of deformation when a force of 10 kgf
(approximately 98 N) was applied in the direction of the arrow
shown in FIG. 5 was measured.
Test Results
[0058] The amount of deformation was 2.44 mm with the foam material
30', whereas the amount of deformation was 1.78 mm with the foam
material 30. Accordingly, in the case of the foam material alone,
it was confirmed that hardness improved approximately 27% with the
foam material 30 of the present embodiment compared to the foam
material 30' of the comparative example.
<Test on Amount of Racket Cross-Section Deformation>
Test Method
[0059] FIG. 6 is a schematic diagram showing aspects of the test on
the amount of racket cross-section deformation.
[0060] The respective foam materials were provided inside the frame
10 (the face portion 12), and the amount of deformation when
applying a force of 50 kgf (approximately 490 N) toward the
interior of the face portion 12 was measured.
Test Results
[0061] The amount of deformation was 0.51 mm with the comparative
example (the foam material 30'), whereas the amount of deformation
was 0.41 mm with the present embodiment (the foam material 30).
Accordingly, it was confirmed that an improvement of approximately
12% with respect to the amount of racket cross-section deformation
was achieved with the foam material 30 of the present embodiment
compared to the foam material 30' of the comparative example.
<Racket Bending Deformation Test>
Test Method
[0062] FIG. 7 is a schematic diagram showing aspects of a racket
bending test.
[0063] The areas where the respective foam materials were provided
in the frames 10 (the face portions 12) were cut to a length of 100
mm, and the amount of bending was measured when supporting the two
ends and applying a force of 50 kgf (approximately 490 N) to the
center.
Test Results
[0064] The amount of bending was 0.73 mm with the comparative
example (the foam material 30'), whereas the amount of bending was
0.69 mm with the present embodiment (the foam material 30).
Accordingly, it was confirmed that an improvement of approximately
5% with respect to the amount of racket bending deformation was
achieved with the foam material 30 of the present embodiment
compared to the foam material 30' of the comparative example.
[0065] As described above, the tennis racket 1 of the present
embodiment includes the frame 10 that surrounds the hitting face
for hitting a ball, and the foam material 30 is provided inside (in
hatched portions) the frame 10 on the two sides of the frame 10
that are on opposite sides of an area of the hitting face on the
tip side than the sweet spot S. In this way, the strength of the
areas on the respective sides of the frame 10 is increased. This
enables to improve the rigidity and vibration absorption when
hitting a ball with the tip side of the hitting face. Also, since
the foam material 30 is not provided in the other areas (the
non-hatched portions), the face portion 12 can be allowed to flex
by an appropriate amount when hitting a ball, and ball control can
be improved. It is also possible to achieve a reduction in weight
compared to the case of providing the foam material 30 in the
entire frame 10.
Variation
[0066] The following describes a modified example of the present
embodiment. In the above-described embodiment, the foam material
was not provided in the non-hatched areas (non-hatched portions)
(the interior of the frame 10 was hollow in the non-hatched
portions) of the frame 10 of the tennis racket shown in FIG. 1.
However, in this modified example, a foam material (foam material
32) different from the foam material 30 is provided in the
non-hatched portions.
[0067] The foam material 32 is a foam material (which corresponds
to a foam body for filling) formed into a sheet shape using a
material whose hardness is different from that of the foam material
30. Note that the hardness of the foam material 32 is lower than
the hardness of the foam material 30.
[0068] FIG. 8 is an illustrative diagram of a method for
manufacturing the variation of the present embodiment.
[0069] As shown in FIG. 8, the foam material 30 is arranged on the
carbon sheet 44 at positions corresponding to the hatched portions,
and the foam material 32 is arranged on the carbon sheet 44 at
positions corresponding to the non-hatched portions in FIG. 1. The
following manufacturing method is similar to that of the
above-described embodiment. In this way, whereas the foam material
was not provided in the non-hatched portions of the frame 10 of the
tennis racket 1 shown in FIG. 1 (the interior of the frame 10 was
hollow in the non-hatched portions) in the above-described
embodiment, a foam material (the foam material 32) different from
the foam material 30 is provided in the non-hatched portions in
this modified example. Since the foam material 30 and the foam
material 32 have different hardnesses, the strength can be changed
according to the position in the frame 10.
[0070] With this modified example, the rigidity of the hatched
portions can be increased, while the non-hatched portions are
prevented from being hollow. This enables to prevent chips, foreign
particles, and the like from entering the frame 10 when the holes
for the insertion of the string are formed in the face portion 12,
for example.
[0071] Note that although the foam material 32 is provided to all
of the non-hatched portions in this modified example, the modified
example is not limited to such. For example, the foam material 32
may be provided on only the tip side of the tennis racket 1 (the
range between the two areas where the foam material 30 is
provided).
[0072] Also, the amount of foam material 30 used (the density
thereof) in the hatched portions of the tennis racket 1 in FIG. 1
may be different from the amount of foam material 30 used (the
density thereof) in the non-hatched portions. For example, a
configuration is possible in which a thinly-formed sheet of the
foam material 30 is arranged in the lengthwise direction of the
carbon sheet 44, and then the foam material 30 is further arranged
thereon in areas corresponding to the hatched portions (the
positions where the foam material 30 is arranged in FIG. 3A) . The
strength can be changed according to the position in the frame 10
in this case as well.
Other Embodiments
[0073] The above-described embodiment is for facilitating
understanding of the present invention, and is not intended to
limit the interpretation of the present invention. As a matter of
course, the present invention can be changed and modified without
departing from spirit the invention, and equivalents thereof are
encompassed in the present invention.
<Foam Material 30>
[0074] In the above-described embodiment, the foam material 30 is
obtained by mixing a resin-based adhesive and a thermally
expandable foam material, and forming the mixture into a sheet
shape, but the present invention is not limited to this. The foam
material 30 may be configured from other compositions as long as it
can be formed into a sheet shape and expands (foams) due to heat or
the like.
<Position where Foam Material 30 is Formed>
[0075] In the above-described embodiment, the foam material 30 was
provided to areas on the two sides of the face portion 12 that are
on opposite sides of an area on the tip side than the sweet spot S
(the areas of the face portion 12 that correspond to the range from
angle .theta..sub.1 to angle .theta..sub.2 in FIG. 1), but the
present invention is not limited to such. For example, in a case
such as when the sweet spot S is frequently used, the foam material
30 may be provided to the two sides of the face portion 12 that are
on opposite sides of the sweet spot S. Also, the area of the
hitting face between the sweet spot S and the base side (side
closer to the grip portion 14) is often used in the case of volleys
performed mainly by middle-aged players, for example. In this case,
the foam material 30 may be provided in areas on the respective
sides of the face portion 12 that are on opposite sides of that
area on the base side. Note that in the present embodiment, the
areas where the foam material 30 is formed in the frame 10 (the
face portion 12) are determined by the positions where the foam
material 30 is arranged on the carbon sheet 44, thus making it is
possible to easily change the positions where the foam material 30
is formed.
* * * * *